Field of the Invention
The present invention relates to a toner for developing an electrostatic charge image to be used in image forming methods, such as electrophotography and electrostatic printing.
Description of the Related Art
As an electrophotographic apparatus using a toner, there are given a laser printer and a copying machine. As a request from users with respect to electrophotographic apparatus, such as a copying machine and a printer, in recent years, there is a demand for the provision of downsizing, high durability for supporting high-speed printing, and an image of stable quality not depending on a usage environment (temperature, humidity).
In electrophotography, a toner charged positively or negatively is carried on a toner bearing member, an elestrostatic charge image-bearing member is charged to form a potential difference between an image portion and a non-image portion, and a toner on the toner bearing member is developed onto the image portion of the elestrostatic charge image-bearing member. The developed toner on the elestrostatic charge image-bearing member is subjected to a step (transfer step) of transferring the toner onto a transfer member, such as paper, or an intermediate transfer member and further transferring the toner onto a transfer member, and is fixed onto the transfer member with heat and pressure.
When a toner image formed on the elestrostatic charge image-bearing member by performing development is transferred onto the transfer member in the transfer step, a transfer residual toner may remain on the elestrostatic charge image-bearing member. In this case, it is necessary to clean the elestrostatic charge image-bearing member with a cleaning device to recover the transfer residual toner into a waste toner container. However, due to the presence of the cleaning device and the waste toner container, the apparatus is increased in size, and the increase becomes an obstacle for downsizing the apparatus. Therefore, there is a demand for further improvement of transferability in order to achieve downsizing of the apparatus.
Further, when a toner is transferred from the photosensitive member onto the transfer material, the amount of a toner that remains on the photosensitive member without being transferred onto the transfer member, that is, the transfer residual toner changes depending on the transfer current. In general, there is an optimum range of the transfer current in which the amount of the transfer residual toner becomes minimum. When the transfer current is lower than the optimum current range, a transfer electric field is small relative to attraction force between the toner and the photosensitive member, and hence the toner does not move and the amount of the transfer residual toner increases.
Meanwhile, when the transfer current is larger than the optimum current range, discharge occurs in a toner layer to rather decrease the transfer electric field, and hence the amount of the transfer residual toner is increased. Thus, it is desired that the transfer current be set to the lowest within the optimum current range.
However, the optimum current range changes also depending on the charge quantity of a toner. In particular, when printing is not performed for a long period of time under high humidity, a reduction in charge quantity, and a change in attraction force between the toner and the photosensitive member are liable to occur, and hence the optimum range of the transfer current is liable to change. In order to address this change, there is a method involving determining a transfer current with an environment detection device, such as a temperature and humidity sensor. However, there is a concern that various control devices may be complicated and increased in size. Therefore, there is a demand for a toner having satisfactory transferability within a wide transfer current range without a change in charge quantity even under high temperature and high humidity.
Hitherto, as a method of improving transferability, there has been given a method involving sticking an external additive to the surface of a toner particle to decrease physical adhesive force between a toner and a photosensitive member. However, when an image is printed on a large number of sheets, the external additive is embedded or detached to make a reducing effect on the adhesive force insufficient, and hence it is difficult to keep transferability. As a method of improving transferability, a method has been considered, which involves uniformly covering the surface of a toner particle with a silicon compound.
In Japanese Patent Application Laid-Open No. H03-089361, as a method of covering the surface of a toner particle with a silicon compound, there is a disclosure of a method of producing a polymerized toner by adding a silane coupling agent to a reaction system.
Further, in Japanese Patent Application Laid-Open No. H09-179341, there is a disclosure of a polymerized toner having on the surface thereof a coating film of a reaction product of a radical reactive organosilane compound.